Structural and functional identification of the pituitary adenylate cyclase-activating polypeptide receptor VPAC2 from the frog Rana tigrina rugulosa

Abstract

Recently, a frog pituitary adenylate cyclaseactivating polypeptide (PACAP)/vasoactive intestinal peptide (VIP) receptor (fPVR) has been characterized, and interestingly, this receptor exhibits characteristics of both mammalian PACAP type II receptors VPAC 1 R and VPAC 2 R. In order to investigate the receptors responsible for mediating the actions of VIP and PACAP in amphibians, in this report, a frog VPAC 2 receptor (fVPAC 2 R) cDNA was isolated. fVPAC 2 R shares 47·7, 46·9 and 62·5% amino acid sequence identity with fPVR, human VPAC 1 R and human VPAC 2 R respectively. Functionally, fVPAC 2 R, when expressed in CHO cells, was responsive to both frog peptides including VIP, PACAP38 and PACAP27 where the EC 50 values of these peptides in intracellular cAMP production were 0·15, 0·18 and 0·16 µM respectively. The pharmacological profiles of human peptides (VIP, PACAP38 and peptide histidine methionine) to stimulate frog and human VPAC 2 Rs were compared, and it was found that these peptides could only activate the frog receptor at micromolar concentrations. fVPAC 2 R was found to be widely distributed in various peripheral tissues as well as several regions of the brain. The presence of the receptor transcripts suggests the functional roles of the receptor in mediating the actions of PACAP and/or VIP in these tissues. As VIP and particularly PACAP27 are highly conserved peptides in vertebrate evolution, comparative studies of these peptides and their receptors in non-mammalian vertebrates should provide clues to better understand the physiology of these important peptides in human and other vertebrates.

Pituitary Adenylate Cyclase-Activating Polypeptide and Its Receptors: 20 Years after the Discovery

“…Although these receptors are structurally similar to mammalian VPAC2-R, they exhibit highest affinity to PHI and peptide histidine valine (Tse et al, 2002). In contrast, the pharmacological profile of the frog VPAC2-R characterized in R. tigrina rugulosa is similar to that of the mammalian VPAC2-R (Hoo et al, 2001). These findings suggest that the common ancestral receptor for VPAC2-R/PHI-R was originally a functional PHI/peptide histidine valine receptor in early vertebrates and that this receptor has evolved to become a VIP/PACAP receptor only after divergence of the tetrapod lineage.…”

Newly-identified receptors for peptide histidine-isoleucine and GHRH-like peptide in zebrafish help to elucidate the mammalian secretin superfamily

“…Also, in the N-terminal extracellular domain that is fundamental for VIP binding (Laburthe et al 2003), the zebrafish sequence is missing a potential glycosylation site, which is expressed in the human, chicken, and frog VPAC2R (Hoo et al 2001). N-glycosylation sites are critical for ligand binding and correct delivery to plasma membrane of the human VPAC1R (Couvineau et al 1995(Couvineau et al , 1996.…”

Identification of a Potential Receptor for Both Peptide Histidine Isoleucine and Peptide Histidine Valine

“…By degenerate PCR and cDNA library screening techniques, we isolated a putative G protein-coupled receptor that shared the highest amino acid identities with the frog [56% (36)] and human [54%, (37)] VPAC2-Rs. Phylogenetic analysis also grouped this receptor with the VPAC2-R to form a distinct subbranch within the receptor superfamily (data not shown).…”